1. Field of the Invention
This invention relates to tool couple elements and in particular to those attached to a vise or to a cylindrical workpiece for holding a threading die in contact with the workpiece while the die is used to form the initial threads thereon.
2. Description of the Prior Art
The cutting of the initial thread on a pipe in a manual operation requires the operator to push the die onto the pipe while simultaneously turning the die handle. This operation is at times a very difficult and awkward task because a large amount of pressure must, on occasion, be exerted on the die against the pipe in order to cut the initial threads. As a consequence, only persons of superior strength are capable of threading pipe.
Typically, difficulties are experienced in forming the starting thread when the pipe lacks close tolerance in roundness. Such out-of-roundness may be caused by the techniques employed in its manufacture, by rough handling, or by deformation of the pipe end as it is being cut. Usually, if the initial attempt to form a thread is unsuccessful, the operator finds that successive attempts also fail; the die merely continues to cut a steep chamfer or bevel on the leading edge of the pipe.
To remedy such a situation, those operators fortunate enough to have a grinding wheel close at hand fashion a slight taper on the outer surface of the pipe so that the cutting edges behind the anterior cutting edge of the die, as well as the latter edge, are engaged in the initial cutting action. However, the operation of shaping a taper is time-consuming and often impractical.
Too frequently, frustrated operators resort to hammering a die onto the end of a pipe in order to start the die. Such hammering usually destroys an expensive tool, the threading die.
The awkwardness of the process of trying to press the die against the pipe and to rotate the die handle simultaneously is further compounded when one attempts to thread the end of an installed pipe. In the past, most operators have elected to wrench out the section of pipe which must be cut and re-threaded. The pipe-fitting activity associated with removing such a section of pipe can be time-consuming and costly, especially when the joint connecting the section to other pipe is relatively inaccessible.
In my patent identified above, there has been disclosed a tool couple for pushing a threading die onto the unthreaded outer surface of a cylindrical workpiece without damaging the cutting edges of the die and for subsequently maintaining sufficient force on the die to prevent it from slipping as it is turned to cut the initial threads in the workpiece. This tool couple comprises a frame with an elongated arm and a shaft supported thereby for moving a rotatable member in a direction parallel to the longitudinal axis of the elongated arm. The face of the rotatable member which is adapted for physical contact with the threading die has a generally flat surface. With this rotatable member, care must be taken in aligning the tool couple and the workpiece to prevent the rotatable member from moving sideways as it is being turned.